The present invention is generally directed to a process for recycling paper broke containing a wet strength additive. More particularly, the present invention is directed to a process for recycling paper broke containing a wet strength additive by mechanically fiberizing the broke into substantially discrete fibers. Once recycled into discreet fibers, the broke can then be used in forming any paper product, such as wipers and tissues.
During the production of tissue and paper products, significant amounts of scrap material are accumulated. This waste product, also known as broke, is generated from products that do not fall within manufacturer""s specifications or from excess paper remaining after the finished product is completed. Since broke is essentially unused raw material, a process to recycle it for future use would eliminate the inefficient disposal of a valuable source of papermaking fibers.
Problems have been experienced in the past, however, in being able to reuse the paper fibers contained in broke. For instance, prior to using broke for making a commercial tissue, wiper or other similar product, it is necessary to treat the fiber source to chemically degrade unwanted chemical constituents which may adversely affect the quality of the recycled paper product. Notable examples of contaminants that must be removed from broke before the broke can be recycled are wet strength additives. Wet strength additives are added to fibers during the wet end process of the papermaking procedure to increase the strength of tissue and paper products when wet. Examples of wet strength additives include but are not limited to polyamines, urea-formaldehyde, melamine-formaldehyde, alkaline-curing polymeric amine-epichlorohydrine, ketene dimers and glyoxalated polyacrylamide resin.
Historically, permanent wet strength broke has been broken down and recycled using chemical processes. Specifically, there have been three types of chemical processes employed for repulping permanent wet strength broke. The purpose of each of the chemical treatments is to aid in degrading the wet strength chemistry so the mechanical action of the pulper rotor can degrade the tissue or paper into individual fibers suitable for reuse in other products. The first and most effective of these chemical processes to remove wet strength additives includes treating the broke with hypochlorite, chlorine, or hypochlorous acid, depending on reaction conditions in the hydrapulper, to chemically oxidize the wet strength resin molecule and thus allow the tissue to be further broken down by the shearing and mechanical action of the pulper rotor. The - disadvantages of this process include potential chloroform generation, loss of brightness on unbleached fiber, and increased potential for corrosion of the paper machine.
Another chemical process entails treatment of the fiber with caustic and high temperature to swell the wet strength tissue structure such that the mechanical action of the hydrapulper can defiberize the sheet. Although this process is effective on unbleached grades of fiber, the disadvantages of this procedure are the need for heating the pulpers and the handling of caustic treatments. Caustic can also darken the fibers.
Finally, the third chemical process for repulping permanent wet strength broke includes treating the broke with persulfate salts. As with the other chemical procedures, the treatment with persulfate salts possesses disadvantages such as the need to neutralize residual persulfate, the need for pH and temperature adjustment, and the high cost of chemicals.
Using chemical processes to prepare wet strength broke for recycling can be expensive because of the additional cost of chemicals described in the aforementioned processes. In addition, there are certain types of fibers which cannot be successfully defibered using chemical treatments in the wet state. Also, there are certain grades of wet strength additives that may not be adequately defibered by chemical treatment. Finally, chemical treatments may have unfavorable reactions with the fiber. An example of such a chemical interaction is the yellowing that occurs when mechanically pulped fibers are contacted with hypochlorite, chlorine, hypochlorous acid, or caustic (sodium hydroxide).
Accordingly, there remains a need for a fiberizing process for broke containing wet strength additives that avoids the use of chemical treatments in the wet state.
The present invention recognizes and addresses the foregoing drawbacks, and deficiencies of prior art constructions and methods.
Accordingly, it is an object of the present invention to provide an improved method for recycling broke containing wet strength additives.
Another object of the present invention is to provide a process for recycling broke containing wet strength additives without having to chemically treat the broke.
It is another object of the present invention to provide a method for recycling broke containing wet strength additives by mechanically fiberizing the broke.
Still another object of the present invention is to provide a process for mechanically recycling broke containing a wet strength additive for forming paper products, such as wipers and tissues.
These and other objects of the present invention are accomplished by providing a process for recycling paper containing wet strength additives. The paper containing the wet strength additives can be broke obtained from, for instance, wipers, tissues and other similar paper products. According to the present invention, the paper containing the wet strength additive is mechanically fiberized for a time sufficient to overcome fiber bonds formed by the wet strength additives. Ultimately, the paper is fiberized into substantially discrete fibers. The discrete fibers can then be re-incorporated into a fiber furnish for forming a paper web, which can then be used in forming various products.
The process of the present invention can be used to process papers containing any amount of a wet strength additive. For most applications, however, the paper will contain from about 0.5% to about 5% by weight of the wet strength additive and particularly from about 0.5% to about 2% of the wet strength additive. The wet strength additives present in the paper can vary depending upon the particular application. Examples of wet strength additives include polyamines, urea-formaldehydes, melamine-formaldehydes, epichlorohydrines, ketene dimers, and polyacrylamide resins.
Prior to being fiberized, the paper containing the wet strength additive can be dried and shredded if desired. In general, the paper being fiberized should have a moisture content of less than about 20%, and particularly less than about 15%. Preferably, the paper has a moisture content that is about the same as or less than the moisture content of the atmosphere.
Various devices can be used in order to mechanically fiberize the paper. In general, a mill or pulverizer is used in the process. Specific examples of mills that can be used include a hammermill, a disc mill, a pin mill or a wing beater mill.
Once the paper is recycled into discrete fibers, the fibers can be used to form various products. For instance, the fibers can be incorporated into an aqueous fiber furnish and used to form various paper webs. The fiber furnish can contain recycled broke alone or in combination with other various types of fibers. Products that can be made with the recycled broke include wipers, tissues, and various other similar products.
Other objects, features and aspects of the present invention are discussed in greater detail below.